Hair and evolution 毛發和進化論

為什麼進化後的人類毛發稀疏？而和我們人類最近似的動物王國裡的親戚則仍全身匹著毛發？在物種進化過程中，毛發稀疏的人類是如何確保自己能成功生存下來？本期《隨身英語》談論毛發和人類進化的關系。

課文內容

詞匯: Evolution 進化

Compared to other large mammals on Earth, we humans have relatively little hair. This obvious fact is not so strange until we look at our closest living relatives in the animal kingdom – chimpanzees and other great apes. Why, might we ask, have we evolved to be almost hairless when all other primates are still covered in fur? In fact, bizarre as it may seem, our lack of hair has been the key to our evolutionary success as a species.

The question why our earliest ancestors lost their hair when fur would have been beneficial to them – for keeping warm on cold nights, for example – was pondered by Charles Darwin, the famous evolutionist: “No one supposes that the nakedness of the skin is any direct advantage to man.” He concluded that the reason hominins lost their hair was sexual selection. In other words, we prefer our partners to have little hair. But what caused our ancestors to start losing their hair before this preference set in?

The most likely hypothesis to explain the loss of hair is that it became necessary when early hominids moved to a more open savannah habitat around 2 to 3 million years ago, when they started to hunt big game.Hunting in open savannah meant being exposed to the strong heat of the sun for several hours in the day and being in danger of overheating. Being covered in hair prevented our ancestors from losing heat fast enough. So, as Peter Wheeler, of Liverpool John Moores University in the UK, explained, losing hair allowed them to develop the ability to sweat and therefore to cool down. Early humans could, as a consequence, be out at midday hunting and foraging. “It would be [an] enormous advantage to be able to spend the entire midday foraging, finding mates or fighting enemies”, Tamás Dávid-Barrett of Oxford University says. “Sweating allows that, and for sweat to be efficient you need to be mostly hairless”. The meat from hunting animals gave early humans the energy to fuel their growing brain.

Humans are the sweatiest primates on Earth. They have up to 5 million sweat glands,which produce about 12 litres of sweat per day. It’s this propensity to sweat that accounts for our hairlessness and has allowed us to thrive. It might help to remember this next time you’re surrounded by sweaty hairless torsos in the gym!

詞匯表

primates 靈長目動物
bizarre 奇怪的，離奇的
species （動植物的）物種
to ponder 思索，考慮
evolutionist 進化論者
nakedness 裸露
hominins 古人類
sexual selection 雌雄淘汰
ancestor 祖先
hypothesis 假說，假設
hominids 原人
savannah 稀樹草原
to hunt 打獵
game 野禽
early human 早期人類
foraging 覓食，搜尋食物
find a mate 尋找配偶
gland 腺
propensity 習性，傾向
to thrive 長得健壯
torso （人體的）軀幹

測驗與練習

1. 閱讀課文並回答問題。

1. True or false? All primates are covered in fur.

2. Who was Charles Darwin?

3. Why was moving to the savannah a problem for our early ancestors?

4. What is the advantage of having little hair in a hot climate?

5. What link does the author make between hunting meat and human success?

2. 請你在不參考課文的情況下完成下列練習。選擇一個意思合適的單詞填入句子的空格處。

1. I discovered the other day that I have a __________ relative living in Greenland. She’s actually my first cousin.

direct close good near

2. Darwin explained his famous __________ theory of natural selection in 1859 in his book ‘On the Origin of Species’.

revolutionary evolutionary evolution extraordinary

3. If babies wear too many clothes in hot weather, they are at __________ of overheating.

risk danger likely possibility

4. Daniel __________ hard work. He’s happiest when he’s got lots of problems to solve at the office.

thrives at thrives on thrives with thrive on

5. Our human ancestors lost hair because this allowed them to sweat with the greatest __________.

effort deficiency efficiency sufficiency

答案

1. 閱讀課文並回答問題。

1. True or false? All primates are covered in fur.
False. Humans only have a little hair on their bodies compared to other primates.

2. Who was Charles Darwin?
He was a famous evolutionist.

3. Why was moving to the savannah a problem for our early ancestors?
Because it meant that they were exposed to long hours of strong sun and they were in danger of overheating.

4. What is the advantage of having little hair in a hot climate?
It means that you can sweat efficiently.

5. What link does the author make between hunting meat and human success?
The author explains that eating meat provided energy that helped the brain to develop.

2. 請你在不參考課文的情況下完成下列練習。選擇一個意思合適的單詞填入句子的空格處。

1. I discovered the other day that I have a close relative living in Greenland. She’s actually my first cousin.

2. Darwin explained his famous evolutionary theory of natural selection in 1859 in his book ‘On the Origin of Species’.

3. If babies wear too many clothes in hot weather, they are at risk of overheating.

4. Daniel thrives on hard work.

5. Our human ancestors lost hair because this allowed them to sweat with the greatest efficiency.